During the last few decades, great advances have been made in the construction of prostheses which can be worn by amputees or persons suffering from birth defects in order to allow them to live as normal a life as possible. This is particularly true with respect to leg prostheses and, to a large extent, has resulted from efforts to reduce, as far as possible, the physical incapacity of soldiers injured in combat.
In order to provide as much freedom of movement as possible, a leg prosthesis which is to be worn by a person who has undergone an above-the-knee amputation normally includes a joint which allows flexion, at least to some extent. Flexion is the bending of the knee which, for example, allows the human leg to bend during an activity such as walking.
Prior art prostheses which have included such knee joints have been found to be unsatisfactory in some instances because the knee joint must be capable of allowing at least some flexion, while also being capable of being locked against flexion when the amputee puts his weight on the prosthesis, e.g., when he takes a step. Unfortunately, many presently available prostheses do not allow such freedom of movement. For example, it has been found that some prior art units do not allow the wearer to take as normal a step as possible because the knee joint fails to lock at the proper time. If locking should not occur while the amputee is walking, for example, it is quite likely that the wearer will fall, suffering physical and/or emotional injury. Consequently, it has become desirable to produce a knee joint which allows a considerable degree of flexion, while still allowing the wearer to positively lock the joint against flexion when he takes a step or otherwise puts his weight on it.